Lecturer in Engineering Science

Julian Fells

  • I am an EPSRC Research Fellow in the Department of Engineering Science.

  • I am leading research into novel optical fibre sensors for extreme environments.

  • I am strategic advisor in photonics to the Mathematical Physical and Life Sciences Division.

  • I spent 20 years in industrial research in multi-national and start-up companies.

Julian Fells


At Trinity I teach the first-year and second-year Electrical and Information Engineering papers. In the Department of Engineering Science I supervise fourth-year projects and third-year laboratory classes.I have also taught the third-year option in Circuits and Communications. I supervise DPhil students in areas relating to my research in optical fibre sensors.

Microscope image of the central core of an optical fibre, with an inscribed Bragg grating sensor.
Microscope image of the central core of an optical fibre, with an inscribed Bragg grating sensor.


I lead a research area in optical fibre sensors. We use a femtosecond laser to inscribe novel sensors into optical fibre. Adaptive optics is used to correct for the distortion when focussing inside the fibre. These sensors can measure temperature, strain and pressure and withstand extreme environmental conditions. An optical fibre around 0.1 mm in diameter can have many such sensors along its length, enabling measurements to be made in otherwise inaccessible areas. This data can be used to control propulsion and energy systems, to enable higher efficiency and lower emissions. There are also many applications in healthcare.

Prior to coming to Oxford in 2015, I spent 20 years in industrial research at corporate companies GEC-Marconi and Nortel Networks, followed by start-up companies Splashpower and Stingray Geophysical. My research has encompassed optoelectronic devices, optical fibre devices, optical fibre communications, optical fibre sensors, wireless power, and liquid crystal devices. This has been for diverse sectors, including telecommunications, oil and gas, civil engineering, manufacturing and consumer electronics.

My inventions have been protected by 14 granted patent families and have had significant industrial impact. I devised the first negative chirp electoabsorption modulator which is now a key component in optical networks. I also invented the ultralow power standby found in Qi wireless power chargers, which is incorporated in hundreds of millions of products worldwide.

You can find out more about my work at:



Julian Fells researching

Selected Publications

X. Wang , J.A. J. Fells , T. Ali , J-D. Lin , C. Welch , G.H. Mehl , T.D. Wilkinson , M.J. Booth , S.M. Morris , and S.J. Elston, ‘Transmissive flexoelectro-optic liquid crystal optical phase modulator with 2π modulation’, AIP Advances 10, 055011 (2020); https://doi.org/10.1063/5.0009630

J.A.J. Fells, C. Welch, W.C. Yip, S.J. Elston, M.J. Booth, G.H. Mehl, T.D. Wilkinson, and S.M. Morris, ‘Dynamic response of large tilt-angle flexoelectro-optic liquid crystal modulators’, Opt. Express 27, 15184-15193, 2019. https://doi.org/10.1364/OE.27.015184

JJ Sandford O’Neill, JAJ Fells, C Welch, G Mehl, WC Yip, TD Wilkinson, M.J. Booth, S.J. Elston, and S.M. Morris, ‘Robust measurement of flexoelectro-optic switching with different surface alignments’, J. Appl. Phys. 125, 093104 2019. https://doi.org/10.1063/1.5086241

P.S. Salter, M.J. Woolley, S.M. Morris, M.J. Booth, and J.A.J. Fells, ‘Femtosecond fiber Bragg grating fabrication with adaptive optics aberration compensation’, Opt. Lett. 43, 5993-5996, 2018. https://doi.org/10.1364/OL.43.005993

J.A.J. Fells, et al., ‘Flexoelectro-optic liquid crystal analog phase-only modulator with a 2π range and 1  kHz switching’, Opt. Lett. 43, 4362-4365, 2018. https://doi.org/10.1364/OL.43.004362

J.A.J. Fells, S.J. Elston, M.J. Booth, and S.M. Morris, ‘Time-resolved retardance and optic-axis angle measurement system for characterization of flexoelectro-optic liquid crystal and other birefringent devices’, Opt. Express 26, 6126-6142, 2018. https://doi.org/10.1364/OE.26.006126